A thermoelectric conversion material is a material which can interconvert thermal and electric energies, and constitutes a thermoelectric converter which is used as a thermoelectric cooling element or a thermoelectric power generating element. Thermoelectric conversion material is used for thermoelectric conversion using the Seebeck effect. Thermoelectric converting performance is represented by Formula (I) which is called the performance index ZT.ZT=α2σT/κ  (1)(wherein, α represents the Seebeck coefficient, σ represents the electrical conductivity, κ represents the thermal conductivity, and T represents the measured temperature.)
It is apparent, according to Formula (I), that in order to improve the thermoelectric converting performances of a thermoelectric conversion material, Seebeck coefficient α and electrical conductivity σ of the material are increased, and thermal conductivity κ of the material is decreased. Japanese unexamined patent publication No. 10-242535 describes an addition of fine particles, which is inactive to the base material of the thermoelectric conversion material (inactive fine particle), to the starting material particles in order to decrease thermal conductivity κ of the material. Thereby, the inactive fine particles can scatter phonons, which are the major factor of the thermal conduction in a thermoelectric conversion material, to decrease thermal conductivity κ.
However, in a conventional conversion material in which the inactive fine particles are unevenly distributed, the inactive fine particles, which provide the scattering effect of the phonon, have a large adverse influence on the other physical properties, such as electrical resistivity, due to the uneven distribution thereof, thus an increase in the performance of the thermoelectric conversion materials is inhibited.
Since the thermoelectric conversion material is highly temperature-dependent, the material must be selected according to the temperature at which it is used. For example, Bi2Te2 type material is used in a low temperature range, PbTe type material is used in a medium temperature range, and SiGe type material is used in a high temperature range. In this connection, Japanese unexamined patent publication No. 10-60563 has proposed a composite thermoelectric conversion material wherein atoms are filled in holes in the structure.
According to the art disclosed in Japanese unexamined patent publication No 10-242535 above, the microparticulation of the starting material in addition to the inactive fine particles to be dispersed makes it possible for the inactive fine particles to be easily dispersed in the entirety of the base material, thus leading to a high probability of the presence of the inactive fine particles between the starting material particles, whereby no crystallization of the starting material particles occurs. However, in the known arts shown above, the inactive fine particles are evenly dispersed to adjust other physical properties, which do not directly relate to the equation (1), such as the electrical resistivity, but the electrical conductivity σ and the thermal conductivity κ, both directly relating to the performance index ZT in the equation (1), have not been studied. Therefore, the inactive fine particles in the known arts above have a microscale diameter. The dispersion state of the inactive fine particles has not been precisely studied.
According to the art disclosed in Japanese unexamined patent publication No. 10-60563 above, the compounding extends the effective usable temperature range, but satisfactory properties are not obtained over a wide temperature range.
Therefore, the object of the present invention is to eliminate the drawbacks of the prior art stated above by providing a thermoelectric converter having a good performance index and a wide usable temperature range, and a method for manufacturing the same.